When we think about our mental health, I’m sure most of us don’t think about our gut.

But did you know that your mental well-being may be influenced by the microscopic creatures living in your gut microbiome? The connection between gut health and mental health is one that has recently been gaining more attention, as scientists believe that the gut microbiome has enormous potential to yield new “psychobiotics.”

Psychobiotics are beneficial bacteria (probiotics) or support for such bacteria (prebiotics) that act on your bacteria-brain relationships. (1)

When I say “bacteria-brain relationships”, I’m referring to the “gut-brain axis,” an important concept that I’ve talked about before, but I’ll briefly outline it again below.

The gut-brain axis is comprised of two kinds of nervous systems: the central nervous system (CNS) and the enteric nervous system (ENS).

The CNS consists of the spinal cord and brain, and contains a crucial feature called the vagus nerve. The vagus nerve is the longest cranial nerve you have, running from near the hypothalamus all the way to your intestines where it reaches the other big player in the gut-brain axis, the enteric nervous system.

The ENS is connected to the CNS by the vagus nerve, and this system is embedded in the lining of the gastrointestinal system. The ENS is often called the “second brain” which explains why you can sometimes “feel” your emotions in your gut. Despite the fact that under normal circumstances the ENS is in conversation with the central nervous system, research shows that it is entirely capable of functioning all on its own, even when severed from the vagus nerve that connects it to our brain.

So altogether, we have something that looks something a bit like this:

The researchers who created this diagram used a very fitting analogy to think about our gut microbes, which I find helpful. They described our gut bacteria as “microscopic puppet masters” that can do an amazing number of things that change how our body works.

Microbes can:

Produce toxins in the absence of nutrients that can alter mood.

Change how certain receptors (like taste) work.

Manipulate our brain’s reward pathways.

Hijack neurotransmitter communication between the gut and brain via the vagus nerve.

These effects are represented in the diagram by the hand-controllers that look like a cross, and our little microbes are the ones “running the show.”

Although there are multiple ways that gut microbes can act on the gut-brain axis, the vagus nerve (depicted as the thin, gray lines with tendrils shooting off from the side of inside the torso) has been posited as one of the main pathways since it is the main neural axis between the gut and the brain. (3,4)

We still don’t know entirely know how this communication line works, but we do know that signals can move along the vagus nerve or be carried by chemical messengers (i.e. serotonin), and have the potential to alter brain function and activity.

A Healthy Gut Makes for a Healthy Brain

When they administered oral antibiotics to patients with hepatic encephalopathy (a condition of brain dysfunction from liver insufficiency), it was associated with a dramatic improvement. (5) So, targeting and changing the gut microbiome somehow led to a positive change in brain function.

Lately, there has been more research exploring whether our gut health is tied to neurological disorders such as Parkinson’s disease. (6,7) Unfortunately, it’s still somewhat of a “chicken-or-the-egg” dilemma. Is it

Is it having Parkinson’s that changes our gut? Or is it changes in the microbiome that can predict Parkinson’s? What we do know is that gastrointestinal symptoms (such as inflammation or constipation) can often be the first signs of Parkinson’s, which is a sign that our gut health may very well have a lot to do with our mental health. (8)

One working hypothesis is that, in response to microbial imbalance, certain intestinal microbes release neurotransmitters, or chemical messengers, that can travel down the vagus nerve and alter brain behavior.

It’s important to know that the release of neurotransmitters from both the gut and brain must maintain a careful balance.

If the microbiome churns out too much norepinephrine–a stress hormone–it can ramp up our HPA-axis and result in a larger stress response in our bodies. (9) If the microbiome produces too much or too little serotonin, it could result in changes in sleep, behaviour, mood, and also in some conditions such as autism, since altered serotonin systems have been shown to be associated with these changes. (10,11,12)

Although more research is needed, it’s possible that therapies that regulate microbiome imbalance could help treat or even prevent diseases such as Parkinson’s or Alzheimer’s before neurologic function is compromised. These findings also further highlight the importance of a balanced microbiome for lifelong health.

Gut Microbiota Can Influence Anxiety and Depression

There is increasing data that supports the role of microbiota in influencing anxiety and depressive-like behaviors.

In fact, it has been posited that the gut-brain axis may be the “missing link” in depression. (13) Many researchers have used animal models to demonstrate this link: experimentally elevated stress response and depression in germ-free rats can be reversed by administering a single bacterium like Bifidobacterium infantis, a strain found predominantly in the neonatal intestinal tract. (14,1516)

Clearly, there’s a connection between our gut and how we feel.

So, to dig deeper into this idea, a research team at McMaster University in Toronto discovered that if they colonized the intestines of one type of germ-free mice with bacteria taken from the intestines of another mouse type, the recipient animals would take on aspects of the donor’s personality. Naturally timid mice would become more exploratory, whereas more daring mice would become apprehensive and shy. Pretty cool, huh?

To take it a step further, they took fecal material (that’s right folks, poop) from depressed patients and nondepressed patients; when compared, they found that depressed patients had far less diverse and rich gut microbiota. But what they found next was even more startling. Using lab rats for some classic microbiome meddling, they first gave antibiotics to rats to erase all of their microbiota. Then, they gave these rats a depressed patient’s microbiota via fecal transplant.

The results? When the rats received the transplant from a depressed patient, they became depressed; their cortisol levels and other types of stress hormones increased. Meanwhile, the rats who received a fecal transplant from nondepressed people exhibited no change.

So what does that tell us? Our brain isn’t always culprit behind mental illness, as is commonly thought. It tells us that if there’s mental distress, there’s very likely digestive distress. It’s a two-way street, and both must be addressed.

Improve Your Digestive Health for Better Mental Health

The microbes in our gut have an enormous influence on our brain and behaviors. Luckily, there are some steps that you can take to improve your digestive health.

Choose a diet packed with prebiotic foods. Prebiotics support the growth of beneficial microbes which help regulate and balance our microbiome. You can either get prebiotics from your diet by eating plenty of fruits and vegetables which contain polyphenols and fibers. In addition to this, you may want to consider supplementing with prebiotics. My two favorites are GOS and FOS, which can be found in Galactomune from Klaire Labs and FOS Powder from NOW Foods, respectively.

Eat high-quality fats. Studies of deceased patients with Alzheimer’s found significantly reduced amounts of fats in their cerebrospinal fluid compared with controls. (19, 20) People with low cholesterol are at much greater risk for neurological problems, including depression and dementia. (21)

Manage stress. There is evidence to show that stress (especially if experienced early in life) alters the gut microbiota negatively, and can throw our system off balance. (22) Incorporate mind-body activities like meditation, deep breathing, tai chi, yoga, and more to keep your HPA axis in tip-top shape. Remember, both mental and digestive health need to be functioning optimally for us to feel our best!

I discuss all of this (and more) in my digestive health program, Build Your Biome. Be sure to join me for the next round if you’re interested in building the most robust microbiome possible!

Clearly, our gut health is incredibly important when it comes to mental health. What do you think? Will you change any of your dietary or lifestyle habits to improve your digestive and mental health? Tell me about it in the comments!